Abstract：In acetic acid-sodium acetate buffer solution, eosin Y could emit a stronger fluorescence spectrum at particular excitation wavelength. The fluorescence intensity of this system would be enhanced obviously when a little 8-hydroxyquinoline was added in the solution, while the addition of emulsifier OP could further enhance the fluorescence intensity. If trace lanthanum ion （Ⅲ） were added in this above-mentioned system, the fluorescence intensity would continue to be strengthened, which indicated that lanthanum ion （Ⅲ） played a role of catalyst. Based on this phenomenon, a new system for determination of trace lanthanum was established. In this paper, the influence factors were discussed, such as acidity, reaction temperature and time, reagents dosage and coexisting ions. The optimum reaction conditions, as well as the apparent rate constant and apparent activation energy, were determined. The linear range was 0.2-1.2 μg/mL, and the detection limit was 5.4×10-4 μg/mL. The proposed method could be applied to the determination of trace lanthanum in lanthanum amalgam.
